The teams meet at the Bernabeu on Saturday, with Barca, who led by 12 points at one stage, now four points ahead of Real with five matches to play.
Pep Guardiola's side are still gunning for Champions League glory and also have a King's Cup final against Athletic Bilbao only two weeks away.
"There are too many finals and semi-finals. This is dangerous for a team," Capello told sports daily Marca on Wednesday.
"Although everyone says Barca have a squad of twenty-something players, the truth is there are very few who can really make a difference."
England manager Capello steered Real to an unlikely league title in 2007, when they came back to finish level on points with Frank Rijkaard's Barcelona taking the title on the head-to-head rule on the final day of the season.
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